Dial pulses are two-state or binary d.c. control signals that are used in telephone systems to direct customer cells to the desired destination. As such, they are susceptible to spurious transient pulses produced by equipment which transmits the dial pulses as well as other adjacent equipment in the telephone environment. These spurious pulses are deleterious and can be interpreted as genuine dial pulses.
One area of concern is the tandem interconnection of older trunk circuit equipment, utilizing electromechanical devices, to newer equipment which uses solid state devices. These solid state devices have faster response time than their electromechanical counterparts and therefore may respond to spurious transient signals. Relays within step-by-step outgoing trunk circuits, for example, normally generate transient pulses. These transients can be transmitted over digital facilities, such as T1 carrier, and interpreted as genuine dial pulses by solid state trunk circuits and switching machines in the receiver. This can result in a large volume of misdirected calls.